It wasn't that long ago that women weren't allowed to run while having their period - I guess they thought it would shake things loose unnaturally! Very scary the things women were thought to be "unable to do".
I just found a page about the history of the Boston Marathon -
Boston MarathonWomen weren't allowed to run until 1972.
"Gibb [who snuck in in 1966] had been inspired to run by the return of her race entry with a note saying that women were not physically capable of running a marathon."